Onions 101 – simple techniques to easy nutritious flavorful onions

The basics of growing onions for the homBasics of growing onions for home gardenere gardener

I have had huge success in growing onions but I’ve also had some meager results.  Why you ask?  That’s what I’m going to explore in this post.  The basics of growing onions and problems you may find along the way.

Why grow onions at home?

Infographics about nutrients in shallot bulb. Qualitative vector illustration about onion, vitamins, vegetables, health food, nutrients, diet, etc. It has transparency, blending modes, masks, gradients
Click to enlarge and see the mineral and nutritional value of onions

Onions from home taste better and are more nutritious.

They are easy to grow but do take up valuable space for a long period.  However, onions are so useful to me in the kitchen they are worth the space.  Onions store well in the following order with White storing the longest: Sweet, yellow, red, white.  But you can also harvest one and use it right away in the kitchen or store it in the refrigerator for a few days.

Know the day length of your area

onion day length map
Map from GrowOrganic.com – A company I have purchased onion transplants from in the past.

There are different day-lengths available of onions… in the north we want long-day length varieties.  There are also day-neutral that can grow in the north.  This is very important if you are buying from a catalog.  The length of day is relevant because the bulb/set is triggered to really start growing when the day length changes in late spring.  Prior to that the roots are growing and the plant is becoming potentially stronger, but the visual bulb that we eat doesn’t get going until its triggered by lengthening days.

onion red MGD©

There are a lot of choices to be made with onions.  The main two are variety and then planting type (seed, set, pre-started plants).  I have done all three. I’ve also grown bunching onions, also known as scallions I think, which are onions that wont ever bulb out… they are milder in flavor and very easy to grown inside so you can just pull one out and use it in the kitchen with a salad or as a garnish.


Onion sets:  These look like little onions.  Because they are! Producers start the onions and then force them into dormancy so they can be stored and shipped.  The down side is that typically most garden centers only carry one or two white, yellow, and red variety of sets.  And often they don’t even tell yo the variety and just say “red, yellow or white”.  You can then either plants them shortly before your last frost in the spring, or you can plant them in theonion sets planting fall to get started slowly over the winter IF you live in a mild climate.  Plant them so that the dried up dormant roots are at the bottom and the pointy part is up.  They need only a small amount of soil over them (maybe an inch) and should be about 4-6 inches apart.  Do not skimp on the spacing… I have before and I think it does make a difference in your final onion size.  But it is hard to remember when you are planting that little set that the final product will be much larger.  Sets normally take 3-4 months to grow into full size.


Transplants:  These are plants with green (at least your goal is to get them as green as possible!) stems and a small bulbous area at the bottom.  They really are baby plants and they come in groups.  Often you can get a group of 50 including portions of all three onions colors.  When you buy them they may look a little scrawny, and may not be bright green.  It always worries me to get them this way but… they really do perk up and are fine if you placeonion transplants them in water for at least 24 hours before you plant them.  I have kept them in much longer sometimes… but try not to actually put them into water until you are pretty sure you will be able to plant them in a day.  I do spritz the bundle with water if its going to be longer that a few days before planting.  I will say that some resources say not put them in water before planting… I’ve tried both ways and I think it mainly depends on how strong your transplants are and how moist your soil will be for the first few weeks after you plant.

With transplants you do have more varieties available.  At my garden store I can usually get 4-5 of each type (red, white, yellow).  You still don’t have anywhere near the choices though of seeds.

With transplants you want to dig a furrow (a line in the soil) shallow enough that the bulbous part of the transplant is about 4-6 inches from the next transplant.  Some years I trim down the green parts and some years I don’t.  In part its aesthetic, but I do seem to feel that they grow better when I cut the stem back to about 6 inches.  They avoid falling over and grow straighter.

postcard of onion colors

Seed:  This is where you can really shine if you have a greenhouse or set up inside your house with grow lights.  The variety of seed is wonderful and onions seeds are really easy to grow.  But you do have to start them well in advance of planting outdoors… 8 to 10 weeks in advance and then you will plant them as transplants in the garden about 2 months after the last frost in the pacific northwest to avoid them rotting and sitting in water (earlier if we have a dry spring… like that ever happens!).

The coin is a 10 pence

Harvesting, curing, storing:  The sets and transplants will take 3-4 months to grow into full size.  You will know its time to harvest because the green growth will start to fade or yellow, and the stalk will fall over and they wont grow any larger (don’t try to artificially knock them down… it will only hurt the plant).  Often the neck and top of the onion will start to peak out of the soil so you can gauge the size. You will then want to let the bulb cure in the sun if possible for about 2 days.  Don’t cure in the rain… if there isn’t sun when you cure let them dry in as warm a place as possible. As I said above onions keep in this order with white as keeping the longest: Sweet (higher water content), yellow, red, white.  Onions kept in the dark like perfect conditions of 65 degrees and 75% humidity.  They need good ventilation so hanging them in mesh or nylon materials work well.


Soil:  Onions really need to NOT be sitting in water and must have good Hand Holding Black Soil In The Form Of Heartdrainage.  On the other hand though, onions need a fair amount of water… they are bulbs after all and contain a fair amount of water in their final stage.  Onions like slightly acidic soils but this is not a huge problem.  Make sure your soil is amended with good organic material before planting.  If you planted there last year add a soil amendment (compost or a bag of organic soil amendment).  If you have good soil to begin with you probably only need to fertilized 2-3 times during the growing season with a organic fertilizer higher in nitrogen.

Weeds are a big problem for onions as they don’t like competition.  This last year I inadvertently allowed a weed to go to seed near my onions and it was a bear to handle the competition with the onions… and my onions didn’t win!

Resources for basics of growing onions:

An excellent resource for growing onions and potential problems is this WSU publication Growing Onions in Home Gardens.

Also, this link from a WSU facility in Mt. Vernon, WA shows, using pictures, some of the major diseases and problems of growing onions

If you like onions also try growing garlic at home… 6 steps to growing garlic

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